Solvent drying of coal fines



June 27, 1967 T. J. LAMB ETAL 1 SOLVENT DRYING OF COAL FINES Filed Dec. 28, 1964 DRY COAL FINES 23 SLURRY A f 25 5 WASTE SLUDGE INVENTORS THOMAS J. LAMB EUGENE L. MITCH WILLIAM C. NAUMANN THEIR ATTORNE United States Patent 3,327,402 SOLVENT DRYING 0F COAL FINES Thomas J. Lamb, Springfield, Eugene L. Mitch, Glen Rock, and William C. Naumann, Florham Park, N.J.,

assignors to Shell Oil Company, New York, N.Y., a

corporation of Delaware Filed Dec. 28, 1964, Ser. No. 421,572 8 Claims. (Cl. 349) This invention relates to a process for drying coal fine-s.

More particularly, the invention relates to an improved process for the solvent treatment of coal fines to remove substantial quantities of water contained in the fines.

Commercial methods for mining bituminous-type coal result in the formation of a substantial quantity of minute coal particles, i.e., 10 mesh or less. Subsequent treatment is necessary to eliminate the hazards of these dust size particles while enhancing the attractiveness of the coal product. Present process treatments include (1) underground spraying of the coal product with the Water to remove this dust thereby preventing contamination of the air environment; (2) cleaning of the mined coal by spraying with Water; or (3) subjecting the mined coal to wet screening on such apparatus as a tipple. The moisture retained from any of these Wet treatments must be removed for a number of reasons, including any or all of the following: 1) to avoid freezing difiiculties and to facilitate handling the coal during shipment and transfer to the firebox; (2) to reduce the heat wasted in evaporation of surface moisture on the coal, thus increasing efiiciency and burning; (3) to decrease transportation costs; (4) to improve the coal so that it may be used for specific purposes such as producing coke and briquets; and (5) to facilitate dry cleaning.

Surface moisture can be removed from large coarse coal particles, i.e., greater than mesh, easily by any of the following processes: (1) gravity drainage; (2) mechanical dewatering, e.g., screens, centrifuges or filters; and (3) thermal drying.

However, none of these conventional treatments have proved to be commercially attractive for drying minute coal particles under 10 mesh, i.e., coal fines. These coal fines absorb up to 25% and more of their weight of water during treatment of the coarser coal particles, and do not lend themselves to gravity and mechanical separation. Removal of this absorbed water to obtain a saleable coal through thermal drying has proven to be hazardous and uneconomical. Attempts have been made to salvage a portion of these coal fines, e.g., by a pellitizing operation wherein the fines are bound with lignin and starch and dried. But for the most part, coal fines, which total in excess of 28 million tons per year of recoverable coal, are being discharged as Waste.

It is therefore, a principal object of this invention to remove a substantial portion of the absorbed water from coal fines. It is a further object of this invention to employ a solvent to remove water from a coal fines slurry. These objects will be better understood and other objects will become more apparent from the description of the invention as given hereinafter and by reference to the accompanying drawing wherein:

The single figure is a simplified flow diagram illustrating a preferred mode of operating the invention.

Now, in accordance with this invention, it has been found that the amount of Water retained by coal fines can be substantially reduced to a more desirable range through contact of the Wet coal fines with specific organic solvent, followed by the separation of at least a substantial portion of the water/ solvent solution from the coal fines slurry.

To ensure a more complete recovery of the solvent and inherently greater drying, the coal fines may be additionally thermally treated at a moderate temperature to vaporize the remaining solvent/ water solution absorbed on the filter cake of coal fines. This thermal treatment does not have the inherent hazardous aspect of conventional thermal operations as it is performed at substantially lower temperatures, i.e., a temperature only sufficiently elevated to vaporize the lower boiling solvent.

While the process of the invention is, of course, not in any way limited by any particular theory, it is believed that the solvent displays a greater attraction (aflinity) for Water than do the coal fines and therefore, the solvent washes out the water absorbed in the coal fines. Because of its greater volatility, suitable solvents can be employed which will vaporize at temperatures substantially below the hazardous range and therefore can be easily recovered in substantial quantities.

While the term coal fines is meant to include substantially all the particles up to 10 mesh (1.651 millimeters in diameter), it has been found that about 83% of the particles are less than 0.005 millimeters in diameter and about 99% are less than 325 mesh (0.04 millimeters in diameter).

It is desirable to employ a low-molecular weight organic solvent containing from 1 to 4 carbons, at least one and not more than three oxygens, up to one nitrogen, and the remainder being hydrogen. Halogenated compounds containing carbon, hydrogen and oxygen can be useful but tend to be prohibitively expensive.

It is further desirable that the organic solvents of this invention be at least 10% soluble with water when only interstitial water is to be removed, and preferably as close to completely miscible in all proportions as possible when all the water absorbed in the coal fines is to be removed.

Solvents which have been found to be useful in the drying operation of this invention include the lower molecular weight alkanols, preferably having from 1 to 4 carbon atoms; the lower molecular weight ketones and similar esters.

Examples of suitable highly volatile solvents include methanol, ethanol, propanol, butanol, isopropanol, dimethyl ketone (acetone), methyl ethyl ketone, diethyl ketone and acetonitrile.

Although any amount of solvent which results in removal of a portion of the water present in the coal fines can be employed, advantages of the invention are most evident when the solvent to Water. weight ratio utilized is from 1:1 to 153:1, with 3:1 to 7:1 being the most preferred. Of course, the amount of solvent employed will vary depending on the amount of water which is to be removed from the coal fines. It has been found most ad vantageous to decrease the water content of the coal fines to about 7% rather than drying the fines completely. However, the instant invention could be employed to remove substantially all of the water although concentrations below 7% water by weight in the coal fines tend to produce a dust hazard.

The solid-liquid contacting means can be any conventional apparatus such as an extraction column, rotating 7 disk contactor, etc. The solvent separator also can employ any of the means of separation known to those of skill in the related separation arts, e.g., centrifuges, filters, hydrocyclones, etc.

Thermal drying is not necessary to obtain coal fines containing less than about 7% by weight of water. However, in order to recover the remainder of the solvent, some such additional process may be required, depending on the solvent employed and its related value. The tem perature at which such a drying step is carried out will usually govern the degree of recovery of the solvent.

The auxiliary thermal drying step, when employed, is best performed at about the vaporization temperature of the specific solvent present or at a temperature up to 10 C. in excess of the specific boiling point, and of course, substantially below the vaporization temperature of water. It is preferred to employ solvents which boil below about 100 C. and especially below 80 C. (S.T.P.). For example, when employing acetone with a boiling point of 56.5 C., the thermal drying is advantageously performed at from about 56.5 C. to 665 C., a temperature, far below that at which coal fines become hazardous to handle and, which is required when it is necessary to remove large quantities of water.

Recovery of the solvent from the water (sludge) solvent mixture leaving the separator and/ or thermal dryer can be performed in conventional apparatus, e.g., a distillation column, which are well known to those with skill in the related arts.

Although the process can be carried out at either subatmospheric, atmospheric or superatmospheric pressures, it is advantageous to employ superatmospheric pressures, i.e., from atmospheric (14.7 p.s.i.a.) to 50 p.s.i.a., so that the solvent will be easily condensed.

Example 1 Coal fines, containing 2.0% by weight of water, and acetone in a weight ratio of 625/375 ('3 parts by weight of acetone to 1 part by weight of water in the coal fines) were mixed with stirring for -60 seconds. The mixture was filtered under a vacuum operated at approximately 15 millimeters mercury for 10 minutes. Precautions were taken to safeguard against solvent losses. The water content and acetone content of the filter cake were found to be 5.3% by weight and 6.3% by weight, respectively. The filter cake was then placed in an oven and heated to 75 C. for about 15 minutes. Analysis for water content reveal 1.2% water by weight in the thermally treated filter cake. An 87% by weight recovery of acetone was obtained.

Examples 11 through X Examples II to X employed operating steps similar to those of Example I and the results are reported, along with the results of Example I, in the following table:

TABLE.SOLVENT DRYING OF WET COAL FINES Water Content of Organic Solvent Weight Filter Cake, (exclusive of Total Ratio of percent w. 11 0) Retained Solvent Systems Solvent] on Filter Cake Recovery, Water in Before Thermal percent w.

Coal Fines Ini- Thermal Drying tial Dry 15 min. percent W.

[37.57 w. acetone I .625%: w. coal fines 3/1 3 2 3 w. acetone... II gzzly coal fines J 5/1 3. 5 2. 5 10. 1 96 5 w. acetone w III g" f l l il fziifi 4/1 2. 7 2. 4 9.0

37.5 w. sopropy a co 0 1v 5, 3 fi y s 3 1 7.1 6.1 17.1 85 50 w. isopropyl alco 01 91 V q coal i l h l (ga:i 5/1 5. 8 4. 6 18. 9 1 9o 58. w. isopropy a co 0 VI w hi l f l l 7 1 5. 2 5.1 17.6 99

.5 w.me y acoio VII 5, 3 E1 i i fi i 3 1 4. 5 3. 4 14.1 86

50 w.me yacoo--- vrrr y coal g h if 5 1 4. 0 2. 9 17. a 95 58. w.me y aco 0 7 5 7 1 2.8 2. 2 11.5 94

31. w. ace one X {68.3% w. coal fines 3/1 4 8 8 a 100 1 Based on anhydrous isopropyl alcohol. 2 Coal fines used in this run had lower initial water content. 5 A plurality of cold traps was employed to safeguard against solvent loss.

Referring to the single figure, the invention will be better understood from the more detailed description made with reference to this specific embodiment. Coal fines in the form of aqueous slurry are introduced via line 1 into a contacting device such as a rotating disk contactor 3. An organic solvent, e.g., acetone, is introduced via line 5. The throughly agitated mixture of slurry and solvent passes from contact means 5 via line 7 to solvent separator 9 from which aqueous solvent is separated and passed through line -11 to the solvent recovery means 13. The coal fines slurry, stripped of a substantial portion of its water content, and preferably having less than about 7% by weight of water, passes via line 15 to a vaporizer 17 wherein substantially all the aqueous solvent remaining with the coal fines is recovered and passed to the solvent recovery means, e.g., distillation column, 13 via line '19. The dried coal fines containing about 7% by Weight of water are recovered via line 21. Solvent recovered in means 13 is recycled via line 23 as makeup solvent to contact means 3. Water and any waste sludge carried over with the solvent is removed from recovery means 13 by line 25. Vaporizer 17 is operated by injection of warm 70 air, preferably waste heat, through line 27.

The following specific examples of the invention are presented to more clearly illustrate the application of the invention, but the details thereof are not to be construed as limiting the invention.

We claim as our invention: 1. A process for removing water from water-containing coal fines having a diameter up to 10 mesh, which comprises,

(a) contacting said coal fines with a low molecular weight organic solvent boiling below about C.,

(b) separating a substantial portion of the, resulting water-containing solvent mixture from the coal fines and (c) vaporing an additional amount of Water-containing solvent off the coal fines from step (b), thereby recovering substantially water-free coal fines.

2. A process in accordance with claim 1 wherein the solvent is selected from the group consisting of al-kanols, ketones and esters.

3. A process in accordance with claim 2 wherein the solvent is methanol.

4. A process in accordance with claim 2 wherein the solvent is isopropanol.

5. A process in accordance with claim 2 wherein the solvent is acetone.

6. A process in accordancewith claim 1 wherein the separation step employs a filtration means.

7. A process in accordance with claim 1 wherein the separation of a substantial portion of the water-containing solvent results in removal of the water in excess of 7% by Weight.

8. A process for removing water from water-containing coal fines, said coal fines having a diameter of up to 10 mesh, which comprises:

(a) contacting said coal fines with a low molecular weight organic solvent containing from 1 to 4 carbon atoms, up to one nitrogen, at least one but no more than three oxygens and the remainder hydro- (b) separating a substantial portion of the resulting Water-containing solvent mixture from the coal fines; 10

(c) heating said separated coal fines to remove an additional portion of water-containing solvent, thereby recovering substantially water-free coal fines; and

(d) treating said water-containing solvent to recover the solvent for recycle to the contacting zone of step (a).

References Cited UNITED STATES PATENTS 1,960,917 5/1934 Nagelvoort 34-9 X 2,553,239 5/1951 Christiansen 349 X 2,567,980 9/1951 Tuomy et a1 34-9 3,252,769 5/1966 Nagelvoort 44-1 FREDERICK L. MATT ESON, JR., Primary Examiner.

D. A. TAMBURRO, Examiner. 

1. A PROCESS FOR REMOVING WATER FROM WATER-CONTAINING COAL FINES HAVING A DIAMETER UP TO 10 MESH, WHICH COMPRISES, (A) CONTACTING SAID COAL FINES WITH A LOW MOLECULAR WEIGHT ORGANIC SOLVENT BOILING BELOW ABOUT 100* C., (B) SEPARATING A SUBSTANTIAL PORTION OF THE RESULTING WATER-CONTAINING SOLVENT MIXTURE FROM THE COAK FINES AND (C) VAPORING AN ADDITIONAL AMOUNT OF WATER-CONTAINING SOLVENT OFF THE COAL FINES FROM STEP (B), THEREBY RECOVERING SUBSTANTIALLY WATER-FREE COAL FINES. 